Potentially Dangerous Move
I totally agree with Dave A - I think this could be a bad move to make in the current ecomonic climate. I am not sure what industry you are in but it is likely that you have competition - this move could provide yet another reason to for your customers to switch suppliers.
As Dave has said, before taking such an action, it is worth the investment in finding out what is causing these "non-revenue generating" calls and seeing how they can be eliminated. Could they be eliminated by proactively contacting people before they call, perhaps by text or email? Could you provide more self service via voice or web if the calls are simple or informational? Do you have inherent internal process, service or product problems that are causing people to call? It's well worth understanding why people call.....
Hope this helps,